TW201328091A - Multi-wavelength DBR laser - Google Patents

Abstract

A multi-wavelength distributed Bragg reflector (DBR) laser diode is provided including front and rear DBR sections and a plurality of dedicated tuning signal control nodes. The front DBR section includes a plurality of front wavelength selective grating sections defining a plurality of distinct grating periodicities λ 1*, λ 2*... corresponding to distinct Bragg wavelengths λ S1*, λ S2*... The rear DBR section comprises a plurality of rear wavelength selective grating sections defining a plurality of distinct grating periodicities λ 1, λ 2... corresponding to distinct Bragg wavelengths λ S1, λ S2... The tuning signal control nodes are associated with corresponding front wavelength selective grating sections, rear wavelength selective grating sections, or both, such that tuning signals applied to one or more of the dedicated tuning signal control nodes spectrally aligns select Bragg wavelengths λ S1*, λ S2*... of the front DBR section with a selected distinct Bragg wavelengths λ S1, λ S2... of the rear DBR section.

Description

Multi-wavelength decentralized Bragg reflector laser [Cross-reference to related applications]

The present application claims priority to U.S. Provisional Application No. 61/556,434, filed on Nov. 7, 2011, and U.S. Application Serial No. 13/570,719, filed on Aug. The contents of the contents are hereby incorporated by reference in their entirety.

The present disclosure relates to laser diodes characterized by multi-wavelength emission, and more particularly to distributed Bragg reflector (DBR) quantum cascade (QCL) laser diodes. Although the concept of the present disclosure will enjoy wide applicability in various fields, the present disclosure also relates to mid-infrared (mid-IR) in, for example, molecular component identification in gas sensing and medical diagnostics. The use of such lasers of tunable sources.

The drawbacks of the prior art still exist. It is an object of the present invention to address such deficiencies and/or to provide improvements over the prior art.

The present disclosure is directed to multi-wavelength DBR QCL products that are operable to sequentially generate a plurality of wavelengths in time. For example, the resulting emission can be used to sample a broad absorption line. Particular embodiments of the present disclosure are limited to unipolar QCLs that use sub-band transitions to produce photons, but it is also intended that the concepts of the present disclosure are suitable for use For bipolar lasers, these bipolar lasers use inter-band transitions to produce photons.

In accordance with an embodiment of the present disclosure, a multi-wavelength decentralized Bragg reflector (DBR) laser diode is provided, the DBR laser diode comprising a front DBR portion and a rear DBR portion and a plurality of dedicated tuning signal control nodes. The front DBR portion includes a plurality of pre-wavelength selective grating portions defining a plurality of different grating periodicities 对应₁ corresponding to different Bragg wavelengths λ _S1 *, λ _S2 *, ... *, Λ ₂ *... The rear DBR portion includes a plurality of post-wavelength selective grating portions defining a plurality of different grating periodicities 对应₁ corresponding to different Bragg wavelengths λ _S1 , λ _S2 . Λ ₂ ...... A plurality of dedicated tuning signal control nodes are associated with respective ones of the pre-wavelength selective grating portions, individual portions of the post-wavelength selective grating portion, or both, and the plurality of dedicated tuning signal control nodes are configured such that One or more of the tuning signals applied to one or more of the dedicated tuning signal control nodes will select the selected wavelengths of the different Bragg wavelengths λ _S1 *, λ _S2 *, ... of the front DBR portion and the latter DBR portion The selected wavelengths in the different Bragg wavelengths λ _S1 , λ _S2 , . . . are spectrally aligned.

A general structure of the multi-wavelength DBR laser diode 10 according to the present invention is shown in FIG. In FIG. 1, the DBR 10 includes a front DBR portion 20 and a rear DBR portion 30, a plurality of dedicated tuning signal control nodes 25, 35, a gain portion 40, a phase portion 50, and a laser diode 10 A waveguide core 45 extending between the front end surface 12 and the rear end surface 14. Gain portion 40 can include a quantum cascade active region and can be positioned between front DBR portion 20 and rear DBR portion 30 along a light propagation axis defined by waveguide core 45 of laser diode 10.

As will be appreciated by those familiar with DBR lasers, the DBR portion of the DBR laser includes a Bragg grating, that is, a retroreflective device based on Bragg reflection by a periodic structure. The periodic structure of the DBR portion defines the Bragg wavelength λ _{B of the} laser. The DBR portion 20 and the rear DBR portion 30 prior to the present disclosure do not rely on the grating phase Φ or periodic or non-periodic shifting in the frequency of the frequency grating to produce multiple wavelength selection capabilities. Further, although the individual reflectance peaks of the front DBR portion 20 can be tuned to match the selected reflectance peaks of the rear DBR portion 30, the respective reflectance peaks of the front DBR portion 20 and the rear DBR portion 30 are spaced such that such The peak reflectances do not overlap each other, as explained in detail below.

This disclosure is directed to the details of the front DBR portion 20 and the rear DBR portion 30. The individual structures of the waveguide core 45, the associated waveguide layer, the gain portion 40 and the phase portion 50, and the anti-reflective coating can be collected from the teachings readily available in the art. As illustrated in Figures 1 and 2, the front DBR portion 20 includes a plurality of pre-wavelength selective grating portions defined to correspond to different Bragg wavelengths λ _S1 *, λ _S2 *. ..... (different Bragg wavelengths) of a plurality of different grating periodic Λ ₁ *, Λ ₂ *. Similarly, the rear DBR portion 30 includes a plurality of post-wavelength selective grating portions that define complex numbers corresponding to different Bragg wavelengths λ _S1 , λ _S2 ... (different Bragg wavelengths) Different grating periodicities Λ ₁ , Λ ₂ ......

As schematically illustrated in FIG. 2, in one embodiment of the present disclosure, each of λ _S1 *, λ _S2 *, ... in a different Bragg wavelength is related to a different Bragg wavelength λ _S1 , λ _S2 ... spectral deviation. However, the wavelength selective grating portion includes dedicated tuning signal control nodes 25, 35 that are separate portions of the dedicated wavelength control node 25, 35 and the pre-wavelength selective grating portion, individual portions of the post-wavelength selective grating portion or The above two are related. In operation, as illustrated in FIG. 3, a tuning signal is applied to one of the dedicated tuning signal control nodes 25, 35 to change a selected one of the different Bragg wavelengths (ie, λ _S3 *) and The selected wavelength is placed to be spectrally aligned with a selected one of the different Bragg wavelengths (i.e., λ _S3 ) to produce an emission at a selected emission wavelength - λ _S3 in the illustrated example. The continuous tuning signal can be adjusted for transmission at successive emission wavelengths λ _S1 , λ _S2 .

In the embodiments shown in Figs. 2 and 3, although each of the different Bragg wavelengths λ _S1 *, λ _S2 *, ... has a different Bragg wavelength λ _S1 , λ _S2 . ..... is shorter, but note that various "untuned" states are intended in accordance with the present disclosure. For example, different Bragg wavelengths λ _S1 *, λ _S2 * . . . may be shorter and/or longer than the corresponding different Bragg wavelengths λ _S1 , λ _S2 . In general, although various control node configurations are intended, the long-wavelength grating portion and the opposite DBR portion of the laser diode are activated by activating a tuning signal control node (eg, a micro-heater or a DC injection electrode) in the short-wavelength grating portion. The corresponding shorter Bragg wavelength gratings are partially aligned.

As a further example, one or more wavelengths of different Bragg wavelengths λ _S1 *, λ _S2 *, ... in the "untuned" state may be related to different Bragg wavelengths λ _S1 , λ _S2 ..... . Spectral alignment. In the "tuned" state, one or more tuning signals can be applied to the dedicated pre-tuning signal control node 25 or the dedicated post-tuning signal control node 30 to change the different Bragg wavelengths λ _S1 *, λ _S2 *. The selected wavelengths in ..... such that all but one of the different Bragg wavelengths λ _S1 *, λ _S2 * ... with respect to different Bragg wavelengths λ _S1 , λ _S2 ..... . Spectral deviation. This configuration and process diagram are shown in Figure 4. In fact, it is ensured that each of the different Bragg wavelengths λ _S1 *, λ _S2 *, ... is spectrally offset from the DBR length of 0.5 mm with respect to different Bragg wavelengths λ _S1 , λ _S2 . Approximately 4.1 cm-1 or more (wavenumber) can be beneficial. Spectral separation should increase with decreasing DBR length.

As further illustrated in Figure 1, the wavelength selective grating portion after the rear DBR portion 30 also has a control mechanism. The control mechanism may take the form of a laser diode heat sink or the illustrated tuned signal control node 35, which may be associated with an individual portion of the wavelength selective grating portion after the rear DBR portion 30. In the case where the laser diode has a heat sink or some other temperature control mechanism common to the front DBR portion 20 and the rear DBR portion 30, it is intended to tune the heat sink temperature, tune the tuning signal control node 25, 35 or above. Both perform thermal control of the front DBR portion 20 and the rear DBR portion 30.

In the case where the pre-tuning signal control node 25 and the post-tuning signal control node 35 include thermal tuning nodes (eg, micro-heater elements), each of the different Bragg wavelengths λ _S1 *, λ _S2 *, ... is ensured It is generally advantageous for a wavelength to be shorter than the different Bragg wavelengths λ _S1 , λ _S2 ... such that an increase in temperature induced by a node in the front thermal tuning node will increase the corresponding tuning wavelength, thereby The respective tuning wavelength is aligned with the target emission wavelength. It is also intended that the pre-tuned signal control node 25 and the post-tuned signal control node 35 can include electrical contacts for DC injection into the front wavelength selective grating portion and the rear wavelength selective grating portion. Finally, it is intended that the individual nodes of the tuning signal control nodes 25, 35 can operate together as a single control node depending on the operational requirements of the particular application.

In the case where the gain portion 40 of the laser diode 10 is characterized by a wavelength dependent optical gain spectrum, it is generally preferred to arrange the wavelength selective grating portion before the front DBR portion 20 and the wavelength selective grating portion after the rear DBR portion 30, So that the grating portion corresponding to the reflectance peak in the relatively lower gain portion of the optical gain spectrum is positioned relatively close to the gain portion 40 of the laser diode 10, corresponding to the relatively higher gain portion of the optical gain spectrum The grating portion of the reflectance peak is located relatively far from the gain portion 40 of the laser diode 10.

The waveguide core 45 of the laser diode 10 can comprise a stack of quantum cascade cores and each quantum cascade core can be configured to define a gain peak that approximates a different Bragg wavelength λ _{S1 of the} post-wavelength selective grating portion One of the wavelengths of λ _S2 . Alternatively, the waveguide core 45 of the laser diode 10 may comprise a single quantum cascade core having a gain spectrum which is sufficiently wide to include different Bragg wavelengths λ _S1 , λ _S2 ... of the post-wavelength selective grating portion. .. In many cases, the gain portion 40 of the laser diode 10 will be characterized by a wavelength dependent optical gain spectrum. To account for this situation, it is intended to place a quantum cascade core having a relatively low optical gain close to the center of the optical propagation mode of the laser diode 10, and a quantum cascade having a relatively high optical gain. The core is placed at the center of the optical propagation mode relatively far from the laser diode 10. Alternatively or additionally, a core having a relatively low optical gain may be constructed with a greater number of levels or higher limiting factors, and a core having a relatively higher optical gain may be constructed with a reduced number of stages or a lower limiting factor. . As a further alternative, it is intended that the shorter wavelength core can be placed near the center of the waveguide core 45 with the longer wavelength core on the outside because the optical mode size at longer wavelengths is greater than the optical mode size at relatively short wavelengths.

Preferably, the waveguide core 45 of the laser diode 10 comprises a monopolar QCL that uses sub-band transitions to produce photons. However, it is also intended that the waveguide core 45 of the laser diode 10 can comprise a bipolar laser that uses a transition between the bands to produce photons.

By way of example and not limitation, in one implementation of the concept of the present disclosure, different Bragg wavelengths λ _S1 , λ _S2 ... are selected as sampling wavelengths of relatively wide absorption lines, ie, approximately 150 Cm ^-1 spectrum width. To this end, Figures 2 and 3 illustrate five reflection peaks that can be generated using five 0.75 mm long post-wavelength selective grating portions selected to match the five absorption peaks of glucose. It should be noted that the power required for the shorter DBR portion of the thermally tuned wavelength is less than the power required for the longer DBR portion of the thermally tuned wavelength. In general, the front wavelength selective grating portion is shorter than the latter portion to allow for higher output power. In a more specific implementation, assuming a grating length of 0.5 mm, the spectral distance between the Bragg wavelength of the selected grating portion and the first null of the DBR is about 4.1 cm ^-1 (ΔβL = 2πn _g ΔwL). For sampling wavelengths outside the grating bandwidth of the sampling wavelength in the rear DBR section, the front reflectance peak should be set to be shorter than one of the post-sampling wavelengths by approximately 4.1 cm ^-1 so that micro-heaters can be used Or DC injection heating to tune each sample wavelength to match the nearby sampling wavelength. The thermal tuning efficiencies determined by the use of microheaters or current injections from 4.57 μm DBR QCL are approximately 11 cm ^-1 W ^-1 mm and 15 cm ^-1 W ^-1 mm, respectively. The heating power required to align the Bragg wavelength of the 0.5 mm long front grating with one of the sampling wavelengths using microheaters or current injection, respectively, is estimated to be 186 mW and 137 mW.

It should be noted that when terms such as "preferably", "commonly" and "generally" are used herein, the terms are not used to limit the scope of the claimed invention or to imply certain features to the structure of the claimed invention. Or the function is critical, basic or even important. Rather, the terms are only intended to identify a particular embodiment or an alternative feature or additional feature of the present disclosure, which may or may not be used in a particular embodiment of the present disclosure.

For purposes of describing and defining the present invention, it is noted that the terms "substantially" and "approximately" are used herein to mean the inherent degree of uncertainty, value, measurement, or other representation attributable to any quantitative comparison. The terms "substantially" and "approximately" may also be used herein to indicate the degree. Quantitative representations of the degree can be varied from the stated reference without causing a change in the basic function of the subject matter in question.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) The detailed disclosure of the present disclosure, and by reference to the specific embodiments of the present disclosure, The details are not to be construed as implying that the details are in terms of the elements of the basic components of the various embodiments described herein. Rather, the scope of the invention is to be construed as the invention Further, it will be apparent that modifications and variations are possible without departing from the scope of the invention as defined in the appended claims. More specifically, although some aspects of the present disclosure are identified herein as preferred or particularly advantageous, it is intended that the present disclosure not be limited to such aspects.

It should be noted that one or more of the following request items use the term "where" as a transitional idiom. For the purposes of defining the present invention, it should be noted that this term is incorporated in the scope of the patent application as an open transitional idiom for introducing a reciting of a series of characteristics of the structure, and the idiom should be used most often. The open preposition term "contains" is interpreted in the same way.

10‧‧‧Multi-wavelength decentralized Bragg reflector (DBR) laser diode

12‧‧‧ front end

14‧‧‧ rear end face

20‧‧‧Pre-DBR section

25‧‧‧Pre-tuning signal control node

30‧‧‧DBR part

35‧‧‧ Rear Tuning Signal Control Node

40‧‧‧ Gain section

45‧‧‧Waveguide core

50‧‧‧ phase part

The following detailed description of the specific embodiments of the present disclosure is best understood by the following description, in which the same structures are designated by the same elements and wherein: FIG. 1 is a multi-wavelength decentralized Bragg reflection according to the present disclosure. mirror (DBR) Schematic diagram of a quantum cascade laser diode; FIG. 2 illustrates characteristics of a grating portion and a back grating portion before untuned multi-wavelength DBR according to the present disclosure; FIG. 3 illustrates one according to the present disclosure A method of tuning a multi-wavelength DBR of an embodiment; and FIG. 4 illustrates a method of tuning a multi-wavelength DBR in accordance with an alternate embodiment of the present disclosure.

10‧‧‧Multi-wavelength decentralized Bragg reflector (DBR) laser diode

12‧‧‧ front end

14‧‧‧ rear end face

20‧‧‧Pre-DBR section

25‧‧‧Pre-tuning signal control node

30‧‧‧DBR part

35‧‧‧ Rear Tuning Signal Control Node

40‧‧‧ Gain section

45‧‧‧Waveguide core

50‧‧‧ phase part

Claims (20)

A multi-wavelength decentralized Bragg reflector (DBR) laser diode comprising a front DBR portion and a rear DBR portion, a plurality of dedicated tuning signal control nodes, a gain portion, and a laser portion a waveguide core extending between the front end surface and the rear end surface of the polar body, the DBR laser diode being characterized in that the gain portion includes an active region and the gain portion is along the waveguide core through the laser diode Defining a light propagation axis positioned between the front DBR portion and the rear DBR portion; the front DBR portion comprising a plurality of front wavelength selective grating portions, the plurality of front wavelength selective grating portions being defined to correspond to different Bragg wavelengths _a plurality of different grating periodicities S ₁ *, Λ ₂ * ... of _S1 *, λ _S2 * ...; the latter DBR portion includes a plurality of post-wavelength selective grating portions, the plurality of The post-wavelength selective grating portion defines a plurality of different grating periodicities Λ ₁ , Λ ₂ ... corresponding to different Bragg wavelengths λ _S1 , λ _S2 , ...; the plurality of dedicated tuning signal control nodes Individual parts of the pre-wavelength selective grating portion Individual portions or both of the post-wavelength selective grating portions are associated, and the plurality of dedicated tuning signal control nodes are configured to be applied to one or more of the dedicated tuning signal control nodes the tuning signal or a plurality of such part of the front DBR different Bragg wavelength λ _S1 *, λ _S2 * ...... selected one of the wavelength of the DBR section after these different Bragg wavelengths λ _S1, λ _S2 One of the selected wavelengths spectrally aligns different Bragg wavelengths. The laser diode of claim 1, wherein: the front wavelength selective grating portion or the rear wavelength selective grating portion and the dedicated front tuning signal control node or the dedicated post tuning signal control node are configured to And causing a tuning signal applied to one of the dedicated pre-tuning signal control nodes or the dedicated post-tuning signal control node to select one of the different Bragg wavelengths λ _S1 *, λ _S2 * Aligned with a selected wavelength spectral pattern of one of the different Bragg wavelengths λ _S1 , λ _S2 ; and the different Bragg wavelengths λ _S1 *, λ _S2 * ... are different than the different Bragg wavelengths λ _S1 , λ _S2 is shorter or longer. The laser diode of claim 2, wherein the pre-wavelength selective grating portion and the post-wavelength selective grating portion are configured with the dedicated pre-tuning signal control node and the dedicated post-tuning signal control node to Applying to a tuning signal of a dedicated pre-tuning signal control node or a dedicated post-tuning signal control node associated with a shorter wavelength, one of the different Bragg wavelengths λ _S1 *, λ _S2 * ... The selected wavelength is placed in alignment with a selected wavelength spectrum of one of the different Bragg wavelengths λ _S1 , λ _S2 . The laser diode of claim 2, wherein each of the different Bragg wavelengths λ _S1 *, λ _S2 *, ... is associated with the respective different Bragg wavelengths λ _S1 , λ _S2 ... spectrally deviates from the length of one of 0.5 mm DBR by about 4.1 cm ^-1 or more. A laser diode according to one of the preceding claims, wherein one or more of the different Bragg wavelengths λ _S1 *, λ _S2 *, ... with respect to the different Bragg wavelengths λ _S1 , λ _S2 ... spectral alignment; and the pre-wavelength selective grating portions and the dedicated pre-tuned signal control nodes are configured to be tuned to the dedicated pre-tuned signal control node The signal will change the selected wavelength of the different Bragg wavelengths λ _S1 *, λ _S2 *... such that all but one of the different Bragg wavelengths λ _S1 *, λ _S2 *..... Regarding the different Bragg wavelengths λ _S1 , λ _S2 ... spectral deviation. A laser diode according to any one of the preceding claims, wherein: the pre-tuned signal control node comprises a thermally tuned node; and the different Bragg wavelengths λ _S1 *, λ _S2 *... Each of the wavelengths is shorter than the different Bragg wavelengths λ _S1 , λ _S2 ... such that a temperature increase by one or more of the nodes in the front thermal tuning node will increase Different Bragg wavelengths λ _S1 *, λ _S2 *... A laser diode according to any of the preceding claims, wherein the pre-tuned signal control nodes comprise electrical contacts for DC injection into the front wavelength selective grating portions. The laser diode of any one of the preceding claims, wherein: the post-wavelength selective grating portion comprises one or more post-tuning signal control nodes associated with the post-wavelength selective grating portions; And the post-tuning signal control nodes are configured such that one or more of the tuning signals applied to one or more of the post-tuning signal control nodes will change the different Bragg wavelengths λ _S1 , λ _S2 ... One or more wavelengths in .... A laser diode according to one of the preceding claims, wherein a dedicated pre-control node comprises a single control node associated with a single pre-wavelength selective grating portion or with a single pre-wavelength selective grating portion Associated with a plurality of tuning signal control nodes. A laser diode according to any one of the preceding claims, wherein: the waveguide core of the laser diode comprises a stack of quantum cascade cores; and each quantum cascade core comprises a gain peak, The gain peak approximates one of the different Bragg wavelengths λ _S1 , λ _{S2 ,} ... of the post-wavelength selective grating portion. The laser diode of claim 10, wherein: the gain portion of the laser diode is characterized by a wavelength dependent optical gain spectrum; and the quantum cascade core having a relatively low optical gain Positioned relatively close to the center of the optical propagation mode of the laser diode, and the quantum cascade cores having relatively high optical gains are placed relatively far from the laser diode The center of the communication model. The laser diode of claim 10, wherein: the gain portion of the laser diode is characterized by a wavelength dependent optical gain spectrum; and using a relatively high number of levels or a relatively high limiting factor The quantum cascade cores having relatively low optical gains are constructed, and the quantum cascade cores having relatively high optical gains are constructed with a relatively low number of stages or relatively low limiting factors. The laser diode of claim 10, wherein: the relatively short wavelength quantum cascade core is placed relatively close to the center of the optical propagation mode of the laser diode, and is relatively long The wavelength quantum cascade core is placed at a center relatively far from the optical propagation mode of the laser diode. A laser diode according to any one of the preceding claims, wherein the waveguide core of the laser diode comprises a single quantum cascade core having a gain spectrum, the gain spectrum being sufficiently wide to include such The different Bragg wavelengths λ _S1 , λ _{S2 ,} ... of the post-wavelength selective grating portion. A laser diode according to any of the preceding claims, wherein the waveguide core of the laser diode comprises a monopolar QCL that uses sub-band transitions to produce photons. The laser diode according to any one of the preceding claims 1 to 14, wherein the waveguide core of the laser diode comprises a bipolar laser, and the bipolar laser uses a transition between the bands to generate photons. . A laser diode according to any one of the preceding claims, wherein: the gain portion of the laser diode is characterized by a wavelength dependent optical gain spectrum; and the front wavelength selective grating portion and the latter wavelength a selective grating portion disposed along the light propagation axis of the laser diode such that a grating portion corresponding to a peak of a reflectance in a relatively lower gain portion of the optical gain spectrum is positioned relatively close to the laser diode The gain portion of the body, and the grating portion corresponding to the peak of the reflectance in the relatively higher gain portion of the optical gain spectrum is positioned relatively far from the gain of the laser diode section. A laser diode according to any one of the preceding claims, wherein: the gain portion of the laser diode is characterized by a wavelength dependent optical gain spectrum; and a lowest gain portion corresponding to the optical gain spectrum The front grating portion of one of the reflectance peaks is positioned closest to the gain portion along a front of one of the light propagation axes of the laser diode. A laser diode according to any one of the preceding claims, wherein: the gain portion of the laser diode is characterized by a wavelength dependent optical gain spectrum; and the lowest gain portion corresponding to the optical gain spectrum The rear grating portion of one of the reflectance peaks is positioned closest to the gain portion along the rear of one of the light propagation axes of the laser diode. A multi-wavelength decentralized Bragg reflector (DBR) laser diode comprising a front DBR portion and a rear DBR portion, a plurality of dedicated tuning signal control nodes, a gain portion, and a laser portion a waveguide core extending between the front end surface and the rear end surface of the polar body, wherein: the gain portion includes an active region and the gain portion is positioned along a light propagation axis defined by the waveguide core of the laser diode Between the front DBR portion and the rear DBR portion; the front DBR portion includes a plurality of front wavelength selective grating portions, the plurality of front wavelength selective grating portions being defined corresponding to different Bragg wavelengths λ _S1 *, λ _S2 *... a plurality of different grating periodicities Λ ₁ *, Λ ₂ *...; the rear DBR portion includes a plurality of post-wavelength selective grating portions, the plurality of post-wavelength selective grating portions being defined corresponding to different Bragg wavelengths λ _S1, λ _S2 ...... plurality of different grating periodicity Λ _1, Λ ₂ ......; these different Bragg wavelengths λ _S1 *, λ _S2 * .... Each wavelength in .. with respect to the different Bragg wavelengths λ _S1 , λ _S2 ..... Short and spectrally offset; the plurality of dedicated tuning signal control nodes are associated with respective ones of the pre-wavelength selective grating portions, and the plurality of dedicated tuning signal control nodes are configured to be applied to the plurality of One or more tuning signals of one or more of the former dedicated tuning signal control nodes select one of the different wavelengths of the different Bragg wavelengths λ _S1 *, λ _S2 *, ... a selected wavelength of the different Bragg wavelengths λ _S1 , λ _{S2 ,} ... of the post DBR portion is spectrally aligned with different Bragg wavelengths; the waveguide core of the laser diode comprises a quantum cascade core a stack; each quantum cascade core includes a gain peak that approximates one of the different Bragg wavelengths λ _S1 , λ _{S2 ,} ... of the post-wavelength selective grating portion; The gain portion of the laser diode is characterized by a wavelength dependent optical gain spectrum; the quantum cascade cores having relatively low optical gains are placed relatively close to the optical propagation mode of the laser diode Center of The quantum cascade cores having a relatively high optical gain are placed at a center of the optical propagation mode relatively far from the laser diode; and one of the lowest gain portions corresponding to the optical gain spectrum The front grating portion of the peak is positioned closest to the gain portion along a front portion of the light propagation axis of the laser diode.